What slow-growing cancers can cause progressive facial asymmetry over a year without other symptoms, such as (Computed Tomography) CT scan or (Magnetic Resonance Imaging) MRI detectable tumors?

Slow-Growing Cancers Causing Progressive Facial Asymmetry

The most likely slow-growing cancer causing progressive facial asymmetry over a year without other symptoms is pleomorphic adenoma of the parotid or accessory parotid gland, which can present as a painless mass causing facial asymmetry over months to years. 1, 2

Primary Diagnostic Consideration: Salivary Gland Tumors

Pleomorphic adenoma is the most common salivary gland tumor (60-70% of all benign salivary gland tumors) and characteristically presents as a slow-growing painless mass that can cause facial asymmetry over extended periods. 3, 2, 4

Key Clinical Features

• Duration of symptoms typically ranges from 2 to 40 years (mean 17.8 years) before patients seek treatment, making this the prototypical slow-growing facial mass. 5
• The tumor presents as a slowly progressive asymptomatic swelling, most commonly in the parotid gland (70-80% of cases), appearing inferior to the pinna of the ear. 2, 4
• Facial asymmetry develops gradually without pain, facial nerve weakness, or other neurological symptoms in uncomplicated cases. 1, 2

Malignant Salivary Gland Tumors

While pleomorphic adenoma is benign, several slow-growing malignant salivary gland tumors can present similarly:

• Mucoepidermoid carcinoma, adenoid cystic carcinoma, and acinic cell carcinoma are the most common malignant subtypes, though they represent a smaller percentage of salivary gland tumors. 3
• Adenoid cystic carcinoma is particularly notorious for perineural spread, which when present causes facial muscle weakness—but early stages may be asymptomatic. 3
• Low-grade malignant tumors can remain asymptomatic for extended periods before causing pain, facial paralysis, or rapid growth. 3

Recommended Diagnostic Workup

Initial Imaging Strategy

MRI orbits, face, and neck without and with IV contrast is the preferred imaging modality, providing superior soft tissue contrast resolution to delineate tumor extent and distinguish it from surrounding normal tissues. 3

CT neck with IV contrast serves as an alternative or complementary study, particularly useful for evaluating osseous anatomy and when MRI is contraindicated. 3

Tissue Diagnosis

Fine-needle aspiration biopsy coupled with imaging characteristics provides preoperative diagnosis, though definitive diagnosis requires histopathological examination of the excised tumor. 3, 1

Note that fine-needle aspiration has only 60% sensitivity and 46% accuracy in detecting malignant transformation of pleomorphic adenoma, so negative cytology does not exclude malignancy. 5

Critical Warning Signs of Malignant Transformation

Rapid enlargement of a longstanding mass, new-onset pain, or facial nerve palsy are warning symptoms of malignant transformation (carcinoma ex pleomorphic adenoma) occurring in 5-25% of untreated pleomorphic adenomas after 15-20 years. 5, 2

Carcinoma ex pleomorphic adenoma has a 75% five-year recurrence rate and significantly worse prognosis than primary malignancies. 2

Other Slow-Growing Facial Tumors to Consider

Sinonasal Tumors

Inverted papilloma and low-grade sinonasal malignancies (adenocarcinoma, low-grade mucoepidermoid carcinoma) can cause progressive facial asymmetry, though they more commonly present with nasal obstruction or epistaxis. 3

CT maxillofacial demonstrates osseous changes, with slow-growing benign masses showing bony remodeling rather than the lytic destruction seen with aggressive malignancies. 3

Nerve Sheath Tumors

Schwannomas and neurofibromas can present as slow-growing masses, particularly in the parotid region where they may involve the facial nerve, though perineural spread typically causes facial weakness. 3

Critical Pitfalls to Avoid

Do not assume all slow-growing facial masses are benign—even longstanding pleomorphic adenomas can undergo malignant transformation, and early malignant tumors may be asymptomatic. 5, 2

Do not rely solely on fine-needle aspiration to exclude malignancy in salivary gland tumors, as sensitivity is inadequate for definitive diagnosis. 5

Do not delay surgical excision of confirmed salivary gland tumors—early and radical removal is the best prevention of malignant transformation and recurrence. 5, 6

Distinguish between true anatomical facial asymmetry from tumor and functional asymmetry from compensatory head posturing, which can mimic tumor-related asymmetry. 7, 8

Treatment Approach

Complete surgical excision with intact capsule is the standard treatment for pleomorphic adenoma, typically via superficial parotidectomy with facial nerve preservation. 3, 2, 6

For malignant salivary gland tumors, complete surgical resection is standard, with postoperative radiotherapy indicated for stage II-IV high-grade tumors and stage III-IV low-grade tumors. 3